Abstract
The optical properties of the chromium doped spinel type semiconductor α-ZnAl2S4 have been examined over the temperature range 2–540 K. The intrinsic photoluminescence (PL) showed an intense ultraviolet peak at 381 nm at 296 K. From extrinsic absorption and emission spectra the transitions between the ground state A2g4 and the excited levels Eg2, T1g2, T2g2, T2g4, and T1g4 of Cr3+ ions were observed. A fit of the measured temperature dependence of the PL decay, using a four level model, yielded the lifetimes of the Eg2, T1g2, and T2g4 levels and the energy gaps between the Eg2–T1g2 and Eg2–T2g4 states which were found to be very close to the values obtained from steady-state measurements. A configurational coordinate diagram for Cr3+ ions in a α-ZnAl2S4:Cr spinel host has been constructed. Optical gain measurements at 198, 298, and 380 K displayed two separate spectral regions associated to the Cr3+ ions and possibly Cr4+ impurity centers. Gain values of up to 25 cm−1 at 198 K were obtained.
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